Self-healing vitreous composition, method for preparing same, and uses thereof

ABSTRACT

The present invention relates to a self-healing vitreous composition containing a particulate vandium additive, to a method for preparing same, and to the use thereof as a self-healing material, in particular for making seals in devices operating at a high temperature such as fuel oils and steam electrolyzers.

The present invention relates to a vitreous composition containing avanadium-based particulate additive, to its method of preparation and toits use as self-healing material, in particular for manufacturing sealsin devices operating at high temperature, such as fuel cells and steamelectrolyzers.

Glasses and glass-ceramics are rigid materials widely used in industry,especially for producing seals in various devices that have to operateat high temperature, especially between 500 and 900° C. Among suchdevices, mention for example may be made of fuel cells (in particularsolid electrolyte fuel cells or solid oxide fuel cells (SOFCs)) thatoperate at temperatures of 700 to 900° C. and steam electrolyzers thatcan be used for the production of hydrogen and also operate at very hightemperature. In these two particular cases, the anode and cathodecompartments must be separated and gastight because of the presence ofhydrogen and oxygen. During the operation and use of these devices, theglasses and glass-ceramics present therein are subjected to thermalcycles that cause cracks to form. The appearance of these crackstherefore reduces the longevity of the devices incorporating suchmaterials.

Two methods for healing cracks formed in glasses and glass-ceramics havealready been proposed.

The first type of method, called “intrinsic self-healing”, consists,without the addition of any healing additive, in filling the cracks orin repairing the surface state of a material of the glass, glass-ceramicor metal/glass composite type by a simple heat treatment in order tophysically modify the material, usually to soften it. This treatment iscarried out by heating the material or the device containing it to atemperature above the melting or softening point of the material.However, the temperatures used for such melting or softening are usuallyabove the temperatures that the devices incorporating these materialscan withstand, Thus, Liu et al. (Journal of Power Sources, 2008, 185,1193-1200) discuss the heat treatment of SOFC fuel cells that containglass seals based on a mixture of BaO, SiO₂Al₂O₃, CaO and B₂O₃, at atemperature above the creep temperature of the glass in order to repairthe cracks formed, while indicating, however, that one limitation ofthis method is that the need to raise the temperature in order to makethe glass creep causes prejudicial deformations of the system into whichit is incorporated.

The second type of method, called “extrinsic self-healing”, consists inadding a healing additive to the composition of the material whichenables the cracks to be filled by a chemical reaction of said additive.This second method applies to materials of the polymer andceramic/composite type. Thus, patent U.S. Pat. No. 5,965,266 describesthe production of a fibrous material reinforced by a ceramic matrix thatcomprises a self-healing phase containing at least one glass precursor,for example carbon tetraboride (B₄C) or an SiBC system, and free carbon(10 to 35%). An oxidizing atmosphere, at a temperature of at least 450°C. but not exceeding 850° C., causes the carbon to oxidize, therebysubsequently transforming the self-healing phase into a glass so as tofill the cracks possibly present in the material. The above documenttherefore teaches that a composite material containing a glass precursorhaving the ability to be oxidized at a temperature of 850° C. or below,such as a precursor based on boron and/or silicon, is self-healing in anoxidizing atmosphere when the precursor composition used during itsformation contains 15 to 35% carbon. Moreover, White et al. (Nature,2001, 409, 794-797) describe a self-healing polymer material(polydicyclopentadiene) comprising a microencapsulated polymerizableself-healing agent (dicyclopentadiene) which is released upon appearanceof a crack. The presence of a polymerization catalyst (Grubbs catalyst)in the structure of the polymer material is necessary in order to causethe healing agent to polymerize, at room temperature, and to fill thecracks. The material obtained after healing is, however, less resistantthan in the initial state. Moreover, this healing technique must becarried out at room temperature and provides healing at any point in thematerial only if the polymerizable self-healing agent and the catalystare in immediate proximity of each other and both uniformly distributedin the structure of the material.

At the present time, there is therefore no glass or glass-ceramiccomposition having the property of rapidly self-healing at the operatingtemperatures of the devices in which said composition is intended to beused, in particular at use temperatures ranging from 400 to 900° C.Extrinsic self-healing is preferable in order to avoid having to raisethe temperature above the operating temperature of the devices.

The object of the present invention is to provide a glass orglass-ceramic composition having such a property.

One subject of the present invention is a self-healing vitreouscomposition comprising at least one network-forming oxide and optionallyone or more modifying oxides, This composition is characterized in thatit further contains, in the form of solid particles, at least onehealing additive chosen from vanadium and vanadium alloys.

The presence of vanadium and/or a vanadium alloy gives this compositionthe property of being self-healing at temperatures of around 400 to 500°C., i.e. temperatures below those normally employed for nonpolymermaterials according to the intrinsic and extrinsic healing methodsdescribed in the prior art. This property is very advantageous in so faras it enables the longevity of the vitreous composition and the devicesincorporating it to be increased, as it is unnecessary to reachtemperatures above the creep temperature of the vitreous composition inorder to observe heating. The temperatures at which this vitreouscomposition self-heals are also compatible with the normal operatingtemperatures of the devices in which it can be used, thereby preventingthese devices from being degraded during the healing process. Thus, thehealing additive may be chosen depending on the temperature at which itis desired to obtain the healing effect. Finally, and as will bedemonstrated in the examples illustrating the present application, thevitreous composition according to the invention, i.e. containingparticles of vanadium and/or a vanadium alloy as self-heating additive,heals more rapidly than vitreous compositions not according to theinvention since they contain a vanadium-free healing additive such as,for example, B₄C.

The inventors have demonstrated that when cracks form in the vitreouscomposition of the invention, and when this composition is in contactwith gaseous oxygen, the healing additive rapidly reacts with the oxygento form vanadium oxide and possibly other oxides such as, for example,boron trioxide when the vitreous composition contains vanadium in theform of an alloy with another element such as, for example, boron(vanadium boride). The vanadium oxide and the other oxides possiblyformed then enable the crack to be filled, these being perfectlycompatible with the principal components (network-forming and modifyingoxides) of the glassy matrix.

In the context of the present invention, the term “vitreous composition”is understood to mean oxide glasses consisting of a vitreous (amorphous)phase and glass-ceramics consisting of a vitreous phase (of the sametype as the vitreous phase of oxide glasses) and a crystalline phasepresent in the form of crystals dispersed within the vitreous phase.Glass-ceramics result from the controlled devitrification of achemically homogeneous glass via heat treatment at a temperatureappropriate for the formation of crystallization nuclei. This heattreatment is called ceramization.

Also in the context of the present invention, the term “network-formingoxides” is understood to mean oxides of elements that can form, bythemselves, the skeleton (glassy matrix) of the vitreous composition.The network-forming elements most commonly used are silicon Si (in itsoxide form SiO₂) which is the predominant constituent of glassymatrices, boron B (in its oxide form B₂O₃), phosphorus P (in its oxideform P₂O₅) and germanium Ge (in its oxide form GeO₂).

Again in the context of the present invention, the term “modifyingoxides” (or non-network forming oxides) is understood to means oxides ofelements that cannot form a glassy matrix by themselves. These areessentially alkali metal oxides, alkaline-earth metal oxides and, to alesser extent, certain oxides of transition or rare-earth elements. Thealkali metal oxides, also called “fluxes”, are used to lower the meltingpoint of the glassy matrix. They comprise especially sodium oxide(Na₂O), potassium oxide (K₂O), and lithium oxide (L₂O). Other oxides,also called “stabilizers”, are used to modify the physical and/ormechanical properties of the glassy matrix generally attenuated by theaddition of the fluxes. They comprise alkaline-earth oxides such ascalcium oxide (CaO) which increases the chemical resistance of theglass, zinc oxide (ZnO) which increases the brilliance and elasticity ofthe glass, iron oxide (Fe₂O₃) which is both a stabilizer and a pigment,and lead oxide (PbO) which forms part of the composition of the crystaland also lowers the melting point by stabilizing the vitreouscomposition.

According to a preferred embodiment of the invention, thenetwork-forming oxides and the modifying oxides are chosen from oxidesof elements chosen from silicon, boron, phosphorus, aluminum, alkalimetals, alkaline-earth metals, iron and zinc.

According to the invention, the vanadium alloys are preferably chosenfrom alloys composed of vanadium and at least one additional elementchosen from the metallic elements of atomic number 22 to 31, 39 to 42,44, 47 to 51, 82 and 83 and the non-metallic elements of atomic number 5to 7, 13 to 15, 33 and 52.

According to a preferred embodiment of the invention, the healingadditive is chosen from vanadium (V), and vanadium alloys chosen fromvanadium boride (VB), vanadium diboride (VB₂), vanadium tetraboride(VB₄), vanadium carbide (VC), vanadium silicide (VSi₂), vanadiumsulfide, vanadium phosphide (VP) and mixtures thereof. According to oneparticularly preferred embodiment of the invention, the healing additiveis chosen from vanadium, vanadium boride, vanadium carbide and mixturesthereof.

It is possible to modulate the healing temperature depending on thechoice of healing additive. Thus, vanadium (V) oxidizes at 350° C. andupward, VB at 400° C. and upward and VC at 350° C. and upward.

The solid particles of the healing additive that can be used in thevitreous composition of the invention preferably have a mean size ofabout 1 to 60 μm and preferably about 1 to 10 μm.

Within the vitreous composition according to the present invention, thehealing additive preferably represents about 5 to 20% by volume, andeven more preferably about 5 to 10% by volume, relative to the totalvolume of the composition.

Although the healing effect is proportional to the volume content ofhealing additive, the amount of said additive may also be expressed as apercentage by weight. In this case, within the vitreous compositionaccording to the present invention, the healing additive preferablyrepresents about 1 to 4% by weight, and even more preferably about 1 to2% by weight, relative to the total weight of the composition.

In addition to the vanadium-based healing additive, the compositionaccording to the present invention may further contain one or moreadditional healing additives normally used in self-healing compositionsand among these the following may be mentioned, by way of example: boron(B), boron tetraboride (B₄C) boron nitride (BN), silicon nitride (Si₃N₄)and silicon carbide (SiC).

When said additional healing additives are used, they preferablyrepresent about 1 to 4% by weight relative to the total weight of thevitreous composition.

When the self-healing vitreous composition according to the invention isa glass-ceramic composition, it may furthermore contain at least onenucleation promoter, enabling better (more homogeneous) distribution ofthe crystals to be obtained, This is usually a fluoride such as forexample calcium fluoride (CaF₂) or a phosphate, such as for examplelithium phosphate (Li₃PO₄).

The vitreous composition according to the invention may be prepared by amethod which is simple, rapid and inexpensive to implement.

Another subject of the invention is therefore a method of preparing aself-healing vitreous composition (SVC) according to the invention andas defined above, characterized in that it comprises at least thefollowing steps:

-   -   a first step of preparing a putverulent vitreous composition        (PVC) consisting of solid particles, by milling a        non-pulverulent vitreous composition (NPVC) comprising at least        one network-forming oxide and optionally one or more modifying        oxides;    -   a second step of preparing a self-healing pulverulent vitreous        composition (SPVC) by blending the pulverulent vitreous        composition (PVC) resulting from the first step with solid        particles of at least one healing additive chosen from vanadium        and vanadium alloys: and    -   a third step of densifying the self-healing pulverulent vitreous        composition (SPVC) resulting from the second step, by heat        treatment in an inert atmosphere.

According to the invention, the expression “nonpulverulent vitreouscomposition” is understood to mean any glass composition prepared by themelting methods conventionally used to produce glass.

During the first step, the milling of the NPVC is carried out untilsolid particles preferably having a mean size of 1 to 60 μm, and evenmore preferably 1 to 10 μm, are obtained. This milling may be carriedout by any conventional milling technique known to those skilled in theart.

According to the invention, during the second step, the vanadium alloysare preferably chosen from alloys composed of vanadium and at least oneadditional element chosen from the metallic elements of atomic number 22to 31, 39 to 42, 44, 47 to 51, 82 and 83 and the non-metallic elementsof atomic number 5 to 7, 13 to 15, 33 and 52.

During the second step, in addition to the vanadium-based healingadditive, one or more conventional additional healing additives normallyused in self-healing compositions may also be added to the PVC, amongwhich additives the following may be mentioned by way of example: boron(B), boron tetraboride (B₄C), boron nitride (BN), silicon nitride(Si₃N₄) and silicon carbide (SiC).

The blending of the PVC with the solid particles of the healing additive(vanadium-based additive and optionally additional healing additive)during the second step is preferably carried out by the method ofprogressive additions or using a mechanical blender, these two blendingtechniques making it possible in fact to obtain a homogeneousdistribution of the healing additive particles in the PVC.

It is important to carry out the densification third step in an inert(for example argon or nitrogen) atmosphere so as to avoid any prematureoxidation of the healing additive so that this can then react withgaseous oxygen upon appearance of a crack in the self-heating vitreouscomposition of the invention. After densification, the self-healingvitreous composition of the invention can therefore be used in anoxidizing atmosphere without any restriction.

According to one particular and preferred embodiment of the method inaccordance with the invention, the densification heat treatment carriedout during the third step comprises at least:

i) a first substep in which the temperature is rapidly raised, forexample at a rate of about 30° C./min, up to the densificationtemperature of the SPVC, said densification temperature being determinedfrom the dilatometric softening temperature of the NPVC used during thefirst step, or by means of a heating microscope;

ii) a second substep in which the densification temperature ismaintained for a time of about 1 to 2 hours; and

iii) a third substep of cooling down to room temperature, for example ata rate of about 10 to 20° C./min.

According to a first variant of the method in accordance with theinvention, the self-healing vitreous composition is intended to be usedas a seal in a device operating at high temperature (i.e. at atemperature of 400 to 900° C.). In this case, the method in accordancewith the invention further includes, before the densification thirdstep, an additional step of producing the seals by means of the SPVCwithin said device. To do this, the SPVC is used as a conventional glassfrit and then the device in which the seals have been produced undergoesthe densification heat treatment defined above in the third step. Inthis case, the SPVC preferably contains at least one additive chosenfrom slips, binders and sintering aids. The heat treatment of the SPVCis preferably carried out according to a method comprising, apart fromsubsteps i) to iii) detailed above, an additional substep prior tosubstep i), during which the SPVC is slowly heated, for example at arate of about 1° C./min, up to a temperature of about 450° C. Thispreliminary slow heating substep is used to remove the binder from theSPVC.

According to a second variant of the method, the self-healing vitreouscomposition is intended to be produced by itself (not in any device),for example for manufacturing bulk self-healing materials. In this case,the method of preparation according to the invention further includes,before the densification third step is carried out, a step of formingthe SPVC, for example by uniaxial pressing.

When the SVC is a glass-ceramic, the method according to the inventionthen further includes, after the densification third step, a fourth stepof ceramization by heat treatment. The temperature and duration of thisfourth step may be determined by the methods conventionally used in thefield, generally by means of a prior characterization by differentialthermal analysis (DTA).

The final subject of the invention is the various uses of theself-healing vitreous composition according to the invention and asdefined above.

A particular subject is the use of a self-healing vitreous compositionas defined above as self-healing material, especially for themanufacture of seals in devices operating at a temperature of 400° C. to900° C., such as solid electrolyte fuel cells and steam electrolyzers.

Another subject of the invention is the use of a self-healing vitreouscomposition as defined above for the manufacture of a glass orglass-ceramic coating of the enamel type, and especially for themanufacture of a coating for corrosion protection at high temperature(i.e. at a temperature of 400 to 900° C.).

The present invention is illustrated by the following embodimentexample, to which said invention is not limited.

EXAMPLE Preparation of A Self-Healing Glass-Ceramic 1) Preparation ofGlass-Ceramic Compositions Containing Vanadium Boride As HealingAdditive

In this example, a self-healing glass-ceramic was prepared from a glasscomposition (glass 1) derived from a sealing glass-ceramic precursorglass composition from the reference: Lara et al., “Sintering of glassesin the system RO—Al₂O₃—BaO—SiO₂ (R═Ca, Mg, Zn) studied by hot-stagemicroscopy”, Solid State Ionics, 2004, 170, 201-208.

Glass 1 had the following composition, expressed in molar percentages:

-   -   CaO: 14-15;    -   BaO: 28-29;    -   Al₂O₃: 9-10;    -   SiO₂: 47-48.

In the glass 1 composition, the mean size of the particles was about 50μm.

The glass 1 composition was then blended with vanadium boride particleshaving a mean size of 50 μm, in an amount of 10% by volume, using themethod of progressive additions.

The resulting blend (blend 1) was then formed, by uniaxial pressing at apressure of 1000 kg/cm², in a stainless steel cylindrical die (diameter:1.2 cm).

A cylinder of compressed blend 1 having the following dimensions wasobtained: length: 0.7 cm; diameter: 1.2 cm. This cylinder was thendensified at a temperature of 1000° C., in argon, for one hour in anelectric furnace, The density of the glass-ceramic thus obtained (GC 10)was close to 100% of the theoretical density (about 3.75 g/cm³). Thisheat treatment also allowed the glass-ceramization of the material inaccordance with the method explained in Lara et al, (see above).

The glass-ceramics GC 5, GC 15 and GC 20, containing respectively 5%,15% and 20% by volume of vanadium boride per 100 volumes of glass 1composition, were thus prepared under the same conditions.

For comparison, a glass-ceramic containing no vanadium boride (GC 0) wasprepared from the glass 1 composition under the same conditions as thoseused above to prepare GC 10.

2) Illustration of the Self-Healing Properties of the Glass-CeramicsAccording To the Invention

The thermal expansion properties of all these glass-ceramics were thenstudied by thermomechanical analysis using a thermomechanical analyzersold under the name TMA SETSYS by the company SETARAM. The curves wererecorded at a speed of 10° C./min, between 200° C. and 1000° C.

The curves obtained are shown in appended FIG. 1 in which the expansion(in %) is plotted as a function of temperature (in ° C.). In thisfigure, the curve plotted as a continuous line corresponds to GC 0; thedashed curve corresponds to GC 5, the dotted curve corresponds to GC 10;the dot-dash curve corresponds to GC 15 and the double dot-dash curvecorresponds to CC 20.

These curves demonstrate that the thermal expansion properties of theglass-ceramics according to the present invention (GC 5, GC 10, GC 15and GC 20) are not affected by the presence of the vanadium borideparticles as healing additive.

The cylinder of GC 10 was fractured, this fracture had the followingdimensions: total length: 1.2 cm; total depth: 0.7 cm; average width:0.01 cm. The fractured cylinder then underwent a heat treatment for 1 hat 700° C. in static air to simulate the conditions of use. Thistemperature is below the glass transition temperature (T_(g)) of theglass (T_(g)=760° C.) so as to be under conditions where intrinsicself-healing, that is to say by softening, cannot occur.

The appended FIG. 2.a is an optical micrograph (×10 magnification) ofthe glass-ceramic after the heat treatment. The appended FIG. 2.b is amicrograph taken by environmental electron microscopy (×20 000magnification) of the glass-ceramic before the heat treatment (0 min.),after 20 minutes of heat treatment (20 min.) and after 60 minutes ofheat treatment (60 min.).

It may be seen in FIGS. 2.a and 2.b that the oxidation of VB at 700° C.is rapid and leads to self-healing of the crack. Specifically, FIGS. 2.aand 2.b show that the crack is filled with one or more phases resultingfrom the oxidation of VB.

To test the reactivity of the particles of vanadium-based healingadditive according to the present invention, the oxidation temperaturesof vanadium boride (VB) and vanadium carbide (VC) particles alone werecompared, by thermogravimetric analysis in a stream of air (20 cm³/min),using a thermogravimetric analyzer sold under the name TGA SETSYS by thecompany SETARAM, with those of carbon tetraboride (B₄C) and boron (B)particles alone. The appended FIG. 3 shows the oxidation curves obtainedby thermogravimetric analysis (TGA) of these various particlescontaining or not containing vanadium as a function of temperature. Inthis figure, the gain in mass of the particles due to oxidation (in %)is plotted as a function of the temperature (in ° C.). The curve plottedas a continuous line corresponds to VB, the dashed curve corresponds toVC, the dotted curve corresponds to B and the dot-dash curve correspondsto B₄C.

It may be seen that the vanadium-based particles that can be used ashealing additive according to the invention (VB and VC) start to oxidizeat 350° C. in the case of VC and 400° C. in the case of VB, i.e. attemperatures well below the temperatures needed to cause the B4C and Bparticles to oxidize (above 800° C.: temperatures above the softening orcreep temperature of the material into which they are incorporated).

The rate of oxidation of these various particles (VB, VC, B₄C and B) wasalso compared by gravimetric analysis as a function of time. The resultsobtained are given in the appended FIG. 4, in which the ratio Δm/m,corresponding to (the difference (Δm) between the mass of an oxidizedparticle and the mass of an unoxidized particle)/(mass (m) of anunoxidized particle), is plotted as a function of time in minutes. Inthis figure, the curve plotted as a broken line corresponds to VC, thecurve plotted as a continuous line corresponds to VB, the dot-dash curvecorresponds to B₄C and the dotted curve corresponds to B.

From the curves in this FIG. 4 it may be seen that the VB and VCparticles oxidize very rapidly (in a few minutes), whereas the B₄C and Bparticles oxidize significantly more slowly.

All of the results presented in this example show that the presence ofthe particles of vanadium-based healing additive in a glass orglass-ceramic composition according to the invention do not in any wayimpair its thermal expansion properties, and make it possible to inducerapid self-healing of the glass or glass-ceramic at a temperature belowthe melting point of the material (from 350° C. upwards), somethingwhich would not be the case with particles containing no vanadium, suchas B₄C and B particles.

1. A self-healing vitreous composition comprising at least onenetwork-forming oxide and optionally one or more modifying oxides,wherein said self-healing vitreous composition further contains, in theform of solid particles, at least one healing additive chosen fromvanadium and vanadium alloys.
 2. The composition as claimed in claim 1,wherein the network-forming oxides and the modifying oxides are chosenfrom oxides of elements selected from the group consisting of silicon,boron, phosphorus, aluminum, alkali metals, alkaline-earth metals, ironand zinc.
 3. The composition as claimed in claim 1, wherein the vanadiumalloys are chosen from alloys composed of vanadium and at least oneadditional element chosen from the metallic elements of atomic number 22to 31, 39 to 42, 44, 47 to 51, 82 and 83 and the non-metallic elementsof atomic number 5 to 7, 13 to 15, 33 and
 52. 4. The composition asclaimed in claim 1, wherein the healing additive is chosen fromvanadium, and vanadium alloys selected from the group consisting ofvanadium boride, vanadium diboride, vanadium tetraboride, vanadiumcarbide, vanadium silicide, vanadium sulfide, vanadium phosphide andmixtures thereof.
 5. The composition as claimed in claim 4, wherein thehealing additive is selected from the group consisting of vanadium,vanadium boride, vanadium carbide and mixtures thereof.
 6. Thecomposition as claimed in claim 1, wherein the solid particles of thehealing additive have a mean size of 1 to 60 μm.
 7. The composition asclaimed in claim 1, wherein the healing additive represents from 5 to20% by volume relative to the total volume of the composition.
 8. Thecomposition as claimed in claim 1, wherein said composition furthercontains one or more additional healing additives selected from thegroup consisting of boron, boron tetraboride, boron nitride, siliconnitride and silicon carbide.
 9. The composition as claimed in claim 8,wherein said additional healing additives represent from 1 to 4% byweight relative to the total weight of the vitreous composition.
 10. Amethod of preparing a self-healing vitreous composition as defined inclaim 1, wherein said method comprises at least the following steps: afirst step of preparing a pulverulent vitreous composition consisting ofsolid particles, by milling a non-pulverulent vitreous compositioncomprising at least one network-forming oxide and optionally one or moremodifying oxides; a second step of preparing a self-healing pulverulentvitreous composition by blending the pulverulent vitreous compositionresulting from the first step with solid particles of at least onehealing additive chosen from vanadium and vanadium alloys; and a thirdstep of densifying the self-healing pulverulent vitreous compositionresulting from the second step, by heat treatment in an inertatmosphere.
 11. The method as claimed in claim 10, wherein the blendingof the pulverulent vitreous composition with the solid particles of thehealing additive during the second step is carried out by the method ofprogressive additions or using a mechanical blender.
 12. The method asclaimed in claim 10, wherein the densification heat treatment carriedout during the third step comprises at least: i) a. first substep inwhich the temperature is rapidly raised at a rate of 30° C./min, up tothe densification temperature of the self-healing pulverulent vitreouscomposition, said densification temperature being determined from thedilatometric softening temperature of the non-pulverulent vitreouscomposition used during the first step, or by means of a heatingmicroscope; i) a second substep in which the densification temperatureis maintained for a time of 1 to 2 hours; and iii) a third substep ofcooling down to room temperature at a rate of 10 to 20° C./min.
 13. Themethod as claimed in claim 10, wherein the self-healing vitreouscomposition is used as a seal in a device operating at high temperatureand in that said method further includes, before the densification thirdstep, an additional step of producing the seals by means of theself-healing pulverulent vitreous composition within said device andthen the device in which the seals have been produced undergoes saiddensification heat treatment.
 14. The method as claimed in claim 13,wherein the self-healing pulverulent vitreous composition contains atleast one additive selected from the group consisting of slips, bindersand sintering aids.
 15. The method as claimed in claim 13, wherein theheat treatment of the self-healing pulverulent vitreous composition iscarried out according to a method comprising, apart from substeps i) toiii) defined above in claim 12, an additional substep prior to substepi), during which the self-healing pulverulent vitreous composition isslowly heated, at a rate of 1° C./min, up to a temperature of 450° C.16. The method as claimed in claim 10, wherein the self-healing vitreouscomposition is intended to be used for manufacturing bulk self-healingmaterials and in that said method further includes, before thedensification third step is carried out, a step of forming theself-healing pulverulent vitreous composition.
 17. The method as claimedin claim 10, wherein the self-healing vitreous composition is aglass-ceramic and in that said method further includes, after thedensification third step, a fourth step of ceramization by heattreatment.
 18. A method for making a self-healing material, said methodcomprising the step of: employing said self-healing vitreous compositionas defined in claim
 1. 19. The method as claimed in claim 18, saidmethod comprising the step of manufacturing of seals in devicesoperating at a temperature of 400° C. to 900° C.
 20. A method formanufacturing a coating for corrosion protection at high temperature,said method comprising the step of: employing said self-healing vitreouscomposition as defined in claim 1.